Refers to the left side or left-hand side (direction/position).
次の角を左に曲がってください。
Please turn left at the next corner.
左側の席は空いていますか？
Is the seat on the left side free?
右を渡ってから左に入ると短い道になります。
If you go across to the right and then turn left, it becomes a shorter route.
Refers to the left hand itself.
彼は左で字を書く。
He writes with his left hand.
左を怪我したので、しばらく不便だ。
I injured my left hand, so it's inconvenient for a while.
ピアノでは右と左で違う役割を弾き分ける。
On the piano, the right and left hands play different roles.
Refers to the political left (left wing/leftist positions).
会議では左の意見が多かった。
There were many left-wing opinions at the meeting.
彼は学生時代に左に傾倒していた。
He leaned to the left politically during his student days.
An older or dialectal usage meaning a person fond of drinking; a drinker (not common in modern standard speech).
辞書には古く『左』が酒好きの意とあることがある。
Some dictionaries note that historically '左' could mean someone fond of drinking.